[ keith-snook.info ~ Common Emitter Amplifier to Calculate Transistor rbb ]

~ Common Emitter Amplifier ~ Transistor rbb Calculator ~

To be used with a Common Emitter test jig as described Here

Boltzmann Constant — k 1.3806x10-23 J/K    [ Joules/Kelvin ]
Charge on a single Electron — q 1.6022x10-19 C   [ Coulomb or Amperes/sec ]
Measurement device load — RL Ω Parallel with RC assumed a.c. coupled
Collector Resistor — RC Ω Load resistor  [ R& RS assumed = 0 ]
Measured Voltage across RC — VRC V  gives  I= VRC/R=  mA
Measured Voltage Gain AVm  [ affected by high rbb and low ro ]
Noise Voltage at Collector — VNtot µVrms  Enter Measured value @ IC T & Bn
Transistor d.c. current gain — β hFE from data sheets @ IC or measured
Device Temperature — T ˚C    Calculation uses  T =   ˚K
Measurement Noise Bandwidth — Bn Hz — Is not the −3dB BW see Here
Calculated results using the Variables entered above
Voltage Gain neglecting ro — AV V/V = α RC/re
Emitter Internal Resistance — re Ω = VT/IC  VT= kT/q =   mV
Load resistor including ro — RCm Ω       RC∥ RL Ω
Internal Collector Resistor — ro kΩ     VA = ro · IC V
Noise at Collector due to IC — VNIC µVrms = √2 q IBn  · (RCm−re)
Noise at Collector due to RCm — VNRC µVrms = √4 k T Bn RCm
Noise at Collector due to rbb µV = √Ntot−V²NRC−V²NIC = √Nrbb+V²NIB
rbb calculated from √Nrbb+V²NIB Ω    The −ve result 

 

Nota Bene The value of RCm [ RC modified by ro ] must be less than the total collector load RC∥RL ~ The calculated value of rbb must be positive and the negative result negative for the answer to be plausible ~ NaN [Not a Number] may indicate the measured gain or  some other inputs are not correct or a non numeric input was entered

See also ~ rbb calculated from data–sheet values  but check the data–sheet figures are the units  required for the calculator and the bandwidth used for the measurement

 

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